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The CairoOperator class

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Introduction

This is used to set the compositing operator for all cairo drawing operations.

The default operator is CairoOperator::OVER

The operators marked as unbounded modify their destination even outside of the mask layer (that is, their effect is not bound by the mask layer). However, their effect can still be limited by way of clipping.

To keep things simple, the operator descriptions here document the behavior for when both source and destination are either fully transparent or fully opaque. The actual implementation works for translucent layers too. For a more detailed explanation of the effects of each operator, including the mathematical definitions, see http://cairographics.org/operators/.

Class synopsis

CairoOperator {
/* Constants */
const integer CLEAR = 0 ;
const integer SOURCE = 1 ;
const integer OVER = 2 ;
const integer IN = 3 ;
const integer OUT = 4 ;
const integer ATOP = 5 ;
const integer DEST = 6 ;
const integer DEST_OVER = 7 ;
const integer DEST_IN = 8 ;
const integer DEST_OUT = 9 ;
const integer DEST_ATOP = 10 ;
const integer XOR = 11 ;
const integer ADD = 12 ;
const integer SATURATE = 13 ;
}

Predefined Constants

CairoOperator::CLEAR

Clear destination layer (bounded)

CairoOperator::SOURCE

Replace destination layer (bounded)

CairoOperator::OVER

Draw source layer on top of destination layer (bounded)

CairoOperator::IN

Draw source where there was destination content (unbounded)

CairoOperator::OUT

Draw source where there was no destination content (unbounded)

CairoOperator::ATOP

Draw source on top of destination content and only there

CairoOperator::DEST

Ignore the source

CairoOperator::DEST_OVER

Draw destination on top of source

CairoOperator::DEST_IN

Leave destination only where there was source content (unbounded)

CairoOperator::DEST_OUT

Leave destination only where there was no source content

CairoOperator::DEST_ATOP

Leave destination on top of source content and only there (unbounded)

CairoOperator::XOR

Source and destination are shown where there is only one of them

CairoOperator::ADD

Source and destination layers are accumulated

CairoOperator::SATURATE

Like CairoOperator::OVER, but assuming source and dest are disjoint geometries

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